hebcal: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/hebcal - from package: hebcal

You may install the required package with command apt-get install {package}
Error in other languages:
hebcal: bevel nie gevind nie
hebcal: comandă negăsită
hebcal: comando não encontrado
hebcal: commande introuvable
hebcal: command not found
hebcal: käsku ei ole
hebcal: không tìm thấy lệnh
hebcal: komanda nerasta
hebcal: Kommando nicht gefunden.
hebcal: kommandot finns inte
hebcal: komut yok
hebcal: nie znaleziono polecenia
hebcal: níor aimsíodh an t-ordú
hebcal: no se encontró la orden
hebcal: no s'ha trobat l'ordre
hebcal: opdracht niet gevonden
hebcal: parancs nem található
hebcal: perintah tidak ditemukan
hebcal: príkaz nenájdený
hebcal: příkaz nenalezen
hebcal: команда не найдена
hebcal: командата не е открита
hebcal: 命令找不到
hebcal: コマンドが見つかりません